Abradable device on the blower casing of a gas turbine engine

ABSTRACT

The invention concerns a turbine engine with an axis of rotation B comprising a blower casing ( 10 ) and a blower (V) with movable blades ( 17 ). A clearance lies between the internal surface of the casing and the free ends of the blades. A bearing of the blower is connected to fixed parts of the turbine engine by connections such that, in the event of a load on the blower blades, these connections break and the axis of rotation of the blower oscillates about the axis of rotation B. The casing comprises, bonded to its internal surface and over at least part of the extent of the clearance, a layer of thermoformable foam ( 19 ) placed opposite the ends of the blades ( 17 ) of the blower (V). The layer of thermoformable foam ( 19 ) is partly covered with a layer of abradable substance ( 14 ), the thickness of the layer of abradable substance ( 14 ) is such that the free ends of the blades of the blower do not reach the layer of foam during the normal functioning of the turbine engine, and, in the event of a load on the blower, the free ends of the blades at least partly fragment the layer of abradable substance.

FIELD OF THE INVENTION

The invention concerns the field of gas turbine engines, and more particularly gas turbine engine blower casings.

BACKGROUND OF THE INVENTION

In the case of aircraft engines, a bladed blower disc is situated on the rotor part at the inlet to the engine and precedes the bladed discs of the compressor. This bladed blower disc accelerates the air before entering the compressor stages. This bladed blower disc is liable to receive foreign bodies such as ice, birds or others. Because of this, this bladed disc is liable to deform, to cause an imbalance on the blower support shaft and cyclic loads and vibrations communicated by the blower shaft support bearings to the fixed parts of the turbine engine, to which these support bearings are connected.

To prevent communication of these loads and vibrations, it is known from the application FR 2 752 024 how to fit a so-called “fusible” bearing, that is to say the bearing supporting the blower shaft is connected to the fixed parts of the turbine engine by fairly weak connections so that they break as soon as a certain load is exerted on the blower blades. These weak connections can be screw connections for example. Once the connection is broken, the bladed disc of the blower continues to turn freely, which avoids transmitting forces onto the fixed parts of the turbine engine. However, the axis of rotation of the bladed disc of the blower oscillates about the fixed axis of rotation of the turbine engine. This oscillation causes that of the blades, which then violently touch the blower casing. The latter is thus greatly stressed mechanically, or even torn, during these shocks.

To remedy this, panels adhesively bonded to the interior of the blower casing have been developed, these panels being composed of a Nomex honeycomb structure filled with an abradable material, bonded to a glass cloth, itself bonded to an aluminium honeycomb, the whole being bonded to the blower casing. Such a technology is expensive and repairs must be carried out in specialist workshops, particularly in the case of casings with a specific shape, for example conical.

SUMMARY OF THE INVENTION

The present invention aims to improve the situation.

The invention concerns a turbine engine with an axis of rotation comprising a blower casing and a blower with movable blades, a clearance lying between the internal surface of the casing and the free ends of the blades, a bearing of the blower being connected to fixed parts of the turbine engine by connections such that, in the event of a load on the blower blades, these connections break and the axis of rotation of the blower oscillates about the axis of rotation of the turbine engine.

According to a first characteristic of the invention, the casing comprises, bonded to its internal surface and over at least part of the extent of the clearance, a layer of thermoformable foam placed opposite the ends of the blades of the blower, the layer of thermoformable foam being partly covered with a layer of abradable substance, the thickness of the layer of abradable substance being such that the free ends of the blades of the blower do not reach the layer of foam during the normal functioning of the turbine engine, and, in the event of a load on the blower, the free ends of the blades at least partly fragment all the layers of abradable material and thermoformable foam.

Optional characteristics of the turbine engine according to the invention, complementary or in substitution, are set out below:

-   -   the thickness of the layer of foam and of the layer of abradable         substance is such that there exists a clearance remaining         between the free ends of the blades of the blower and the layer         of abradable substance during normal functioning of the engine,         this remaining clearance being sufficiently small to limit the         passage of air in order to preserve a dynamic flow of air whose         path is forced by the blades of the blower,     -   the layer of thermoformable foam consists of preformed sectors,     -   the layer of thermoformable foam is a layer of polyacrylic imide         foam,     -   the layer of abradable substance is made from epoxy resin filled         with glass balls,     -   the layer of abradable substance is made from silicone filled         with glass balls,     -   the layer of abradable substance adheres directly or indirectly         to the layer of thermoformable foam.

BRIEF DESCRIPTION OF THE DRAWINGS

The following figures non-limitingly illustrate embodiments of the invention:

FIG. 1 depicts a view in section of a front part of a turbine engine comprising a blower connected by a fusible bearing to the fixed parts of the turbine engine,

FIG. 2A depicts in section part of the inlet to the gas turbine engine comprising an example of a blower casing according to the prior art,

FIG. 2B depicts in section part of the inlet of the gas turbine engine comprising an example of a blower casing according to the invention,

FIG. 3 is a detail of FIG. 2B representing the interaction between a blower blade and the blower casing according to the invention.

The drawings contain essentially elements of a certain character. They can therefore not only serve to give a better understanding of the description but also contribute to the definition of the invention, where applicable.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 depicts a section of a turbine engine T along its axis of rotation. This section comprises a blower V for accelerating the air before the entry to the stages of the compressor C, and then a high-pressure compressor CC. The blower V comprises a disc provided with blades 17 connected by screwing to the front end BA of a blower shaft AV mounted on a front bearing PAV and a rear bearing PAR as detailed in the application FR 2 752 024. The front and rear bearings are supported by support pieces connected to a fixed part of the turbine engine (the stator), at least one of the bearings being connected by connections which are sufficiently fragile to break when there is an excessive load on a blower blade. Such a bearing is referred to as a “fusible bearing”. These weak connections can be connections by screws whose cross-section is reduced over part of the length of the screw for example. Once the connection is broken, the bladed disc of the blower continues to turn freely, which avoids transmitting forces to the fixed parts of the turbine engine. However, the axis of rotation of the bladed disc of the blower oscillates about the fixed axis of rotation of the turbine engine. This oscillation generates that of the blades, which then violently touch the blower casing. The latter is thus greatly stressed mechanically, or even torn, during these shocks.

As known to persons skilled in the art, FIG. 2A depicts a part of the turbine engine T comprising a blower V followed by a compressor C. This turbine engine part comprises a casing 10 forming the stator part S of the blower V and a casing forming the rotor part R of the turbine engine. The shaft of the rotor part of the turbine engine is driven in rotation by a turbine situated downstream of the compressor. The axis of rotation is denoted B. The external surface of the casing of the rotor part and the internal surface of the casing of the stator part delimit a “flow stream” for the air flow. The bladed disc 18 of the blower V comprising blades 17 is fixed to the rotor R.

The bladed blower disc is situated at the inlet to the engine and precedes the bladed discs of the compressor. In FIG. 2A, the shaft of the blower is assumed to be supported by at least one front bearing PAV forming a fusible bearing. To respond to the impacts of the blades of the blower against the casing 8, there have been developed panels 3 bonded to the inside of this blower casing 10, these panels being composed of a Nomex honeycomb structure filled with abradable material, bonded to a glass cloth, itself bonded to an aluminium honeycomb, the whole being bonded to the blower casing. The thickness of these panels makes it possible to preserve the flow stream so that in normal functioning the ends of the blades of the blower disc do not come into contact with these panels. The technology of the panels in FIG. 2A have drawbacks of cost, and the repair and fitting of these panels must be carried out in equipped workshops. In addition, the materials used are not isotropic, the manufacture of the honeycomb structure for a casing of special shape (for example conical) is more complex because of the mechanical characteristics of this structure and the honeycombs are subject to buckling.

The invention makes it possible to remedy these drawbacks.

As in FIG. 2A, FIG. 2B illustrates a part of a turbine engine T comprising the blower V followed by the compressor C. The bladed disc 18 of the blower V comprising blades 17 is fixed to the rotor R. Reference will also be made to FIG. 3, showing in detail the casing 10 positioned opposite the ends of the blades of the bladed discs 18. In the example in FIG. 2B, the casing 10 has the general shape of a truncated cone whose axis of symmetry coincides with the axis of rotation B of the turbine engine. From upstream to downstream, that is to say the direction of flow of the air flow or from the blower inlet to the compressor inlet, the casing 10 of the blower V comprises a first truncated cone part 20 connected to a ring with a diametral step 21 itself connected to a second truncated cone part 22. The internal surface of the first truncated cone part 20 delimits the air flow stream. The ends of the blades are placed opposite the internal surface of the second truncated cone part 22 and are distant from this internal surface by an internal annular space 15. A clearance e is spoken of, for example of 20 mm between the internal surface of the blower casing and the free ends of the blades.

Over at least part of the internal wall of the second truncated cone part there is bonded a layer of thermoformable foam 19 by means of a film of adhesive 12. In the example in FIGS. 2B and 3, the layer of thermoformable foam has a shape complementary to that of the internal annular space so as to fill the latter. Advantageously, the layer of foam has an axial width lg corresponding at least to the axial width lc along the axis B of the free end of the blades 17 of the blower V. The layer of thermoformable foam 19 is covered with a layer of abradable substance 14, over at least the axial width lc of the ends of the blades. The thickness of the layer of abradable substance is such that the free ends of the blades of the blower do not reach the layer of foam during normal functioning of the engine. Advantageously, the layer of thermoformable foam covered with abradable substance entirely fills the internal annular space and is machined so that there is no discontinuity with the internal surface of the first cone part, the flow stream thus being preserved. More particularly, the thickness of the layer of abradable substance is such that there exists a clearance between the free ends of the blades of the blower and the layer of abradable substance during normal functioning of the engine, this clearance being sufficiently small to limit the passage of air in order to preserve a dynamic flow of the air whose path is forced by the blower blades. Downstream of this layer acoustic panels 13 can be positioned so as to preserve the continuity of the flow stream.

In the example in FIGS. 2B and 3, the width lg is greater than the width lc and the internal annular space 15 is delimited by an upstream stop.

Other embodiments are possible: for example, the blower casing can consist of a single piece (frustoconical, cylindrical or other) with symmetry of revolution covered on its internal surface with a protective screen consisting of a layer of thermoformable foam, itself partly covered with an abradable substance. As previously, the layers of thermoformable foam and abradable substance, referred to as “large clearance” abradable layers, are placed opposite the ends of the blades. The blower casing has a clearance between its internal surface and the free ends of the blades so as to a stick a certain thickness of layers on the internal surface of the casing, for example around 20 mm. The flow stream is preserved by the fitting, upstream and downstream of the protective layers, of acoustic panels for example.

The protection of the casing, in the case of rupture of the breaking connection of the fusible bearing, is effected by the screen consisting of thermoformable foam and the abradable substance. In this case, the bearings of the blower shaft are no longer connected to the fixed parts of the turbine engine and the axis of rotation of the blower oscillates about the axis of rotation B of the turbine engine. The ends of the blades dig into the screen by fragmentation of material. Advantageously, the presence of the layer of thermoformable foam offers resistance to the removal of material which is less than the layer of abradable substance, which allows the pulverisation of all the “large clearance” abradable layers in the event of rupture of the bearing fuses.

To facilitate the fitting of the layer of thermoformable foam, the latter consists of preformed sectors. By way of example, the layer of thermoformable foam is a layer of polyacrylic imide foam. Also by way of example, the layer of abradable substance can be made from epoxy resin loaded with glass balls, silicone loaded with glass balls or any other material having the abrasion properties of an abradable substance.

More particularly, the layer of abradable substance adheres to the layer of thermoformable foam through its adhesive properties and by diffusion in the cells of the thermoformable foam.

By virtue of these layers of “large clearance” abradable, the casing is not damaged during abnormal functioning (for example in the case of ingestion of a foreign body). The use of thermoformable foam allows simple shaping, the machining being able to be carried out before the shaping, for example for a conical blower casing part, with a changing profile. The layers of “large clearance” abradable can be repaired without equipment requiring a dedicated workshop, which offers a saving in time and money.

The thickness of these layers makes it possible to preserve the flow stream so that, in normal functioning, the ends of the blades of the blower disc do not come into contact with these layers.

The invention is not limited to the embodiments of the fixing device described above, solely by way of example, but encompasses all variants which can be envisaged by a person skilled in the art in the context of the following claims.

The invention does not apply solely to the frustoconical-shaped casing but can also apply in the case of all other casing shapes, for example cylindrical. 

1. Turbine engine with an axis of rotation B comprising a blower casing (10) and a blower (V) with movable blades (17), a clearance lying between the internal surface of the casing and the free ends of the blades, a bearing of the blower being connected to fixed parts of the turbine engine by connections such that, in the event of a load on the blower blades, these connections break and the axis of rotation of the blower oscillates about the axis of rotation B, wherein the casing comprises, bonded to its internal surface and over at least part of the extent of the clearance, a layer of thermoformable foam (19) placed opposite the ends of the blades (17) of the blower (V), the layer of thermoformable foam (19) being partly covered with a layer of abradable substance (14), the thickness of the layer of abradable substance (14) being such that the free ends of the blades of the blower do not reach the layer of foam during the normal functioning of the turbine engine, and, in the event of a load on the blower, the free ends of the blades at least partly fragment all the layers of abradable material (14) and thermoformable foam (19).
 2. Turbine engine according to claim 1, wherein the thickness of the layer of foam and of the layer of abradable substance is such that there exists a clearance remaining between the free ends of the blades of the blower and the layer of abradable substance during normal functioning of the engine, this remaining clearance being sufficiently small to limit the passage of air in order to preserve a dynamic flow of air whose path is forced by the blades of the blower.
 3. Turbine engine according to claim 1, wherein the layer of thermoformable foam consists of preformed sectors.
 4. Turbine engine according to claim 1, wherein the layer of thermoformable foam is a layer of polyacrylic imide foam.
 5. Turbine engine according to claim 1, wherein the layer of abradable substance is made from epoxy resin filled with glass balls.
 6. Turbine engine according to claim 1, wherein the layer of abradable substance is made from silicone filled with glass balls.
 7. Turbine engine according to claim 1, wherein the layer of abradable substance adheres directly or indirectly to the layer of thermoformable foam.
 8. Blower casing able to form part of a turbine engine according to claim 1, the casing comprising, bonded to its internal surface, a layer of thermoformable foam intended to be placed opposite free ends of the blades (17) of the blower (V), the layer of thermoformable foam being partly covered with a layer of abradable substance, the thickness of the layer of abradable substance being such that the free ends of the blades of the blower do not reach the layer of foam during the normal functioning of the turbine engine, and, in the event of a load on the blower, the ends of the blades at least partly fragment all the layers of abradable material and thermoformable foam. 